Mixing machines



1964 w. H. TUDOR ETAL 3,160,396 uxxmc MACHINES Filed April 9, 1963' a 7 H 4\\5 a I 7/ United States Patent Ofi ice 3,160,396 Patented Dec. 8,-1964 3,1603% MIXWG MACHENES I William H. Tudor and an Sheppard, Hartley, Stoke-n- Trent, England, assigners to Baker Perkins, Incorporated, Saginaw, Mich.

Filed Apr. 9, 1963, Ser. No. 271,756 7 Claims. (Cl. 259-96) This invention relates to mixing machines of the kind, hereinafter called the kind defined, consisting of a container, usually a vertical cylinder, for liquid material to be mixed and a vertical-axis centrifugal impeller in the lower part of the container.

Usually provision is made for downward axial flow feed of material to the eye of the impeller, such as by a propeller co -axially above the impeller, and mixing is effected by circulation of the material centrally downward and then outward and upward in the container.

A machine of the kind defined is capable of effecting rapid and eflicient mixing if the impeller is driven at a high speed but the mixing is accompanied by considerable aeration of the liquid and for some materials such aeration is unacceptable.

One material for which efiicient mixing but without aeration is required is clay slip, for pottery or porcelain, which is made by mixing clay and water to a smooth slurry or sludge l-ike consistency. Such mixing of clay slip is known as blunging and is carried out in a mixing machine comprising a container in which a rotary stirrer is driven at a relatively low speed, say 30 to 40 r.p.m., so as to avoid aerating the slip. It is necessary to avoid aeration because any air bubbles in the slip cause blow holes when the articles made from or coated with the slip are eventually fired.

Consequently, blunging has usually been regarded as a necessarily slow process, usually requiring some 6 to 8 hours, but the present invention provides a machine in which blunging can be effected, without aeration, much more rapidly, for example in about 1 hour, and more efficiently in terms of the green strength of the ciay slip produced.

The mixing machine of the invention is also suitable for mixing other materials, for example certain types of paint, in which aeration is to be avoided.

According to the invention, in a mixing machine of the kind defined there is provided in the container above the impeller baffie means extending across the line of the rotational axis of the impeller so as to oppose the formation of a deep vortex depression in the material being mixed when the impeller is rotated at high speed.

If, as is usual, a propeller is provided coaxially above the impeller, the propeller is located below or in a gap in the lower part of the baffle or baffles.

By avoiding a deep vortex depression in the material, the induction of air into material moving centrally downwards in the container is avoided and it is found that high speed mixing can be effected without aeration of the material.

A simple preferred form of bafile consists of plates which extend axially and radiate from the line of the impeller axis.

A preferred construction of a mixing machine according to the invention is shown on the accompanying drawing, in which:

FIG. 1 is a sectional side elevation and FIG. 2 is a plan.

The machine as shown comprises a vertical cylindrical container 1 in the base of which there is journalled coaxially a shaft 2 carrying a centrifugal impeller 3 consisting of a disc having impeller vanes on one or both faces. The shaft 2 also carries, above the impeller 3,

an axial flow propeller or feed-screw 4 to deliver material downwardly to the centre or eye of the impeller.

Closely overlapping above the impeller, parallel and coaxial therewith, a circular annular plate 5 with a circular aperture is mounted, by studs 6 upstanding from thebase of the container outside the radius of the im-. peller, and on the annular plate 5 there is mounted on edge a diametral axially-extending baflle plate 7 of which the lower central portion is gapped at 8 to provide a clearance around the axial-flow propeller 4,and above this crosses the line of the impeller axis. The baffle plate 7 extends radially beyond the impeller but short of the cylindrical wall of the container and its axial extent is only a minor part of the depth of the container.

Instead ofthe diametral plate 7, forming two radial baffles, radial plates may radiate from the line of the impeller axis in a three-armed, cruciform or other multiplearm cross-sectional pattern.

Below the container 1, which is supported on a base frame 9, the impeller shaft 2 carries a pulley 10 for a belt-drive from a motor 11 on the same base. Other means for rotating the impeller from beneath may alternatively be provided.

In the base of the container, near the cylindrical wall, a valved outlet (not shown) may be provided for drawing-off mixed material.

The top of the container is open for charging and may be peripherally flanged to receive a cover or lid.

It will be noted that the annular plate 5 is of less diameter than the internal diameter of the container and the arrangement of a baffle plate or plates as described above does not impede flow of material centrifugally from the impeller and upwards at the cylindrical wall of the container.

However, the inward and downward flow of material is constrained to pass to the axial-flow propeller or feed screw in sectors on either side of the baffie plate or plates so that at the surface of the material in the container it is not possible for a vortex depression to develop of such depth that air can be entrained in the material downwardly along the line of the axis of the impeller.

It is not necessary for any baffle plate to extend vertically for even a major part of the depth of the container, the constraint of flow of the material to sectors in the region above the impeller being sufficient to prevent a generally circular flow of the mass of the material which would otherwise produce a vortex depression.

We claim:

1. In a mixing machine: vertical container means including a base and sides for holding liquid material to be mixed; drive shaft means extending upwardly through the base of the container and terminating a substantial distance below the top thereof; radially extending centrifugal impeller means on said drive shaft means terminating peripherally a spaced distance from the sides of the container to permit material to move upwardly at the said sides; and diametrically extending bafiie means stationarily supported in the container means and extending across the axis of said shaft means above said impeller means to oppose the formation of a deep axial vortex depression in the material being mixed when the impeller is rotated at high speed.

2. A mixing machine as claimed in claim 1, in which propeller means for downward flow of material to the impeller is provided coaxially above the impeller and said bafile means has a gap in the lower part thereof in which gap said propeller means is located.

3. A mixing machine as claimed in claim 1, in which said baffie means comprises a plate extending axially, said 7 3 a gap being provided in the lower central portion of said plate. i

.4. A mixing machine as claimed in claim 3,' in which said plate extends radially beyond the impeller but short of the wall of said container and the axial extent of said plate is a minor part of the depth of said container.

5. The combination defined in claim 1 in which said bafiie means includes an annular plate on which a di ametrically and axially extending plate is mounted, the annular plate having an axial opening permitting material to reach said impeller means; V

6; The combination defined in claim 1 in which sup- 7 be mixedjdrive. shaft means extending upwardly in said container and terminating a substantial distance below the top thereof; radially extending centrifugal impeller means on said drive shaft means terminating peripherally a spaced distance from the sides of the container to permit material to move upwardly-at the said sides; and diametrically extending baflle means supported in the container means and extending across the axis of said shaft 5 means above said impeller means to oppose the formation of a deep axial vortex depression in the material being mixed when the impeller is rotated at high speed.

References Cited by the Examiner UNITED STATES PATENTS 198,797 1/78- Davis 259108 718,319 '1/03 Cunningham 25996X 2,212,260' '8/40 Brothman 259l07 5/56 Epprecht 25996'X FOREIGN PATENTS 6/50 Great Britain; 3/58 France;

20 CHARLES A. WILLMUTH, Primary Examiner.

GEORGE J. NORTH, Examiner. 

1. IN A MIXING MACHINE: VERTICAL CONTAINER MEANS INCLUDING A BASE AND SIDES FOR HOLDING LIQUID MATERIAL TO BE MIXED; DRIVE SHAFT MEANS EXTENDING UPWARDLY THROUGH THE BASE OF THE CONTAINER AND TERMINATING A SUBSTANTIAL DISTANCE BELOW THE TOP THEREOF; RADIALLY EXTENDING CENTRIFUGAL IMPELLER MEANS ON SAID DRIVE SHAFT MEANS TERMINATING PERIPHERALLY A SPACED DISTANCE FROM THE SIDES OF THE CONTAINER TO PERMIT MATERIAL TO MOVE UPWARDLY AT THE SAID SIDES; AND DIAMETRICALLY EXTENDING BAFFLE MEANS STATIONARILY SUPPORTED IN THE CONTAINER MEANS AND EXTENDING ACROSS THE AXIS OF SAID SHAFT MEANS ABOVE SAID IMPELLER MEANS TO OPPOSE THE FORMATION OF A DEEP AXIAL VORTEX DEPRESSION IN THE MATERIAL BEING MIXED WHEN THE IMPELLER IS ROTATED AT HIGH SPEED. 